Aliphatic acids: influence on sulfate mobility in a forested Cecil soil

Dissolved organic substances derived from forest litter are believed to influence the retention and movement of SO42- in forest soils. A column study was conducted in which 35SO4 was surface applied to a soil and leached with either low-molecular-weight aliphatic acids (AA) or a forest-litter extract. Oxalic, malonic, and succinic acids were used in the concentration range 8.0 x 10-3 to 1.0 x 10-5 mol L-1. Movement of 35SO4 was determined with column depth, as was the 35SO4 activity in the collected leachates. Labeled SO4 soil movement was found to increase with increasing AA concentration. Leachate 35SO4 activity was observed to increase in the order malonic > succinic > oxalic for acid treatments > 1.0 x 10-4 mol L-1. The 1.0 x 10-5 mol L-1 acid treatments did not result in 35SO4 breakthrough in the soil columns. Reduced exchangeable 35SO4 for organic acid ≥ 1.0 x 10-3 mol L-1 suggests that at high concentrations, aliphatic acids may activate sulfate retention sites in soil, while at lower concentrations these acids may accelerate the movement of 35SO4 in forest soils due to selective organic-acid adsorption by soil components